382 
RAY C. FRIESNER 
maxima and minima in the 24-hour period. He further found that the 
rhythms of the tuber were related to the periodicity of the aerial parts, but 
he thought it also probable that the tuber exhibited a rhythm of its own 
which was more or less obscured by the induced periodicity of the aerial 
parts. In 1901 Miss Gardner (9) reported the results of experiments 
on the growth of roots of Pisiim sativum and Vicia faba. She found that 
roots exposed to the alternation of day and night elongated much more 
rapidly during the day than during the night. But the conditions of the 
experiment were far from normal, viz., seedlings were placed in moist sawdust 
in wooden boxes with one glass face, and were made to grow in a horizontal 
direction. 
A more recent work on elongation of underground parts is that of Kelli- 
cott (14) in 1904. In general, he found that curves for elongation of roots 
grown from bulbs of Allium Cepa exhibited three waves of elongation in 
the 24-hour period. Curves for different individuals were quite similar, 
though differing somewhat in the precise time of their maxima and minima. 
In general, the maxima came in the early morning and late afternoon and 
the minima came near noon and midnight. This work was done in the 
absence of any changes of environment, and hence is the first work definitely 
noting a regular rhythm not induced by external changes. A brief summary 
of the above account of investigations on elongation should note that 
(i) regular daily periodicity exists in the presence of regular daily changes 
in the environment; (2) this periodicity is gradually lost when the plants 
are exposed to constant conditions, though irregular and unsteady variations 
of the type called "autonomic" are reported; (3) the work of Kellicott on 
the root of Allium is the first to note any regularity in elongation of roots 
grown under constant conditions. 
Cell Division 
Lower plants. A great many statements are to be found in the older 
literature in regard to the time of day of nuclear and cell division among the 
Thallophytes. Thus Braun (4) notes that cell division in the formation 
of the gonidia of Draparnaldia mutahilis occurs between 6 A.M. and 1 1 A.M. ; 
of Stigeoclonium protensum, between 6 A.M. and 10 A.M.; of Cladophora 
tuberculata, 8 A.M. to 2 P.M.; cell division in Spirogyra is most rapid during 
the night. Thuret (37) notes that the zoospores of Vaucheria are always 
liberated at about 8 A.M.; those of Cutleria multifida at daybreak; while 
those of Enteromorpha clathrata escape during the afternoon. Famintzin 
(8) corroborates Braun's statement in regard to Spirogyra. Strasburger 
(35) notes that cell division in Spirogyra is most rapid at 10-12 P.M., but 
may be delayed until the following morning if the plants are placed at a 
temperature of 0° to 5° C. during the night. De Wildeman (39), on the 
other hand, was unable to note any sensible difference, between day and 
night, in the rate of division in the cells of Spirogyra. His work was done 
